Question: Solve for $x$ and $y$ using substitution. ${-x-2y = 11}$ ${x = y-8}$
Since $x$ has already been solved for, substitute $y-8$ for $x$ in the first equation. ${-}{(y-8)}{- 2y = 11}$ Simplify and solve for $y$ $-y+8 - 2y = 11$ $-3y+8 = 11$ $-3y+8{-8} = 11{-8}$ $-3y = 3$ $\dfrac{-3y}{{-3}} = \dfrac{3}{{-3}}$ ${y = -1}$ Now that you know ${y = -1}$ , plug it back into $\thinspace {x = y-8}\thinspace$ to find $x$ ${x = }{(-1)}{ - 8}$ ${x = -9}$ You can also plug ${y = -1}$ into $\thinspace {-x-2y = 11}\thinspace$ and get the same answer for $x$ : ${-x - 2}{(-1)}{= 11}$ ${x = -9}$